Thanks for the plethora of info from those with great depths of knowledge --
You know who you are (DOUG, BRIAN!). And...Thanks for leaving the WAR's
(Wise Assed Remarks) out of the discussion! At this point, if you'd like
to throw in any WAR remarks -- feel free! (Now that I have the info I need
my sense of humor is back.)
Jack -- if you have any info I can read please forward.
And just to let those know what I needed the info for....we have a customer
getting unexpected shorts under a connector that was soldered with OA.
It goes away when soldered with NC. Turns out, the component is not designed
in such a way that allows for sufficient cleaning. I soldered one with OA
and tested it and the results showed NaCl outside acceptance levels (23.4ug's)
I haven't gotten around to test ones soldered with NC yet, but, now that
I have info, I'll give it a try. (And yes....I tested the components before
hand to baseline my incoming material!!!!)
Thanks again!
-Carrie
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, April 23, 2003 9:23 AM
To: [log in to unmask]; Morse, Carrie
Cc: [log in to unmask]
Subject: Re: [TN] Omega Testing AND No-Clean
Carrie,
I will try to answer your questions, although requiring me to cease my
smart-ass comments limits my writing flair.....
Brian Ellis has already given a pretty good answer and I will give some of
my viewpoints.
Your question is basically what will low residue fluxes do to the numbers I
get in my cleanliness tester, and what should I do in the ensuing panic?
The answer is that the numbers will get higher. The panic comes when you
try to attach historical numbers and meaning to that increase.
As Brian indicated, the fluxes are not reactivated by contact with
isopropanol. The heat of soldering causes some chemical changes that are
not reversible. The flux residues do not really absorb isopropanol either.
However, isopropanol may solubilize/dissolve the flux residue, which then
makes the extract solution more conductive, which then registers on the
machine. You get an increase in reported level, but it means nothing to
reliability.
Ionic cleanliness testers should not be used for acceptance of product.
They should be used for process control only. Anyone who deals with ionic
cleanliness testing should read through IPC-TR-583, An In-Depth Look at
Ionic Cleanliness Testing. That study, done in the 94-95 time frame,
showed the instruments to have a lack of repeatability and reproducibility,
even on the same machine type. Equivalence factors are bogus. The only
valid use is for process control. If, for a particular assembly, I had a
value of 5 last week, 5 yesterday, and today it is 15, something changed
and I better go figure out what it was.
From my days as a consultant, in the early 90s, when many manufacturers
were transitioning to low residue fluxes, I lost tract of the number of
panic calls when people who were used to seeing 5 started seeing 50. I'll
tell you what I told them, throw out the historical "good" and "bad"
numbers and stop using the machines for product acceptance. Determine what
your new number means with respect to reliability, do designed experiments
to find out the process window around the new number, then use the new
number for process control only. It was harder 10 years ago because the
mil-spec ROSE method was in so many contracts, but most listened. It can
be done.
Your machine is giving you a signal. Consider it an FM signal where mil
specs are AM stations. You have to understand your signal and what it
means.
Your last question related to the freeing of contaminants. I would say
generally this is not a problem, but if you apply high levels of flux to
your assemblies and the ROSE tester dissolves them, there is the
possibility of the flux residues being re-deposited in areas you don't want
them, such as DIPswitches or relays. If your tester has sprays or a
reasonable method of solution agitation, I think the occurrance unlikely.
To rule this out, you can take some DIP switches, run them together with a
flux loaded board. Run surface reflectance FTIR on the contact surfaces
and see if flux residue has been deposited.
As you might guess, I have written several papers and articles on the topic
over the years. If I recall, I bundled them into a ZIP file and gave them
to Jack Crawford for IPC use. He gets calls from newbies in the area all
the time and this is some reading he can give them to educate them on the
issues, usually with the statement "contact Doug for more details".
Maybe Jack can send you this file.
Doug Pauls
Rockwell Collins
Still on my first Diet Dew of the Day
"Morse, Carrie"
<CMorse@CIRTRONIC To: [log in to unmask]
S.COM> cc:
Sent by: TechNet Subject: [TN] Omega Testing AND No-Clean
<[log in to unmask]>
04/22/2003 04:59
PM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to
"Morse, Carrie"
This question goes out to all those with No-Clean Chemistry Experience --
Especially
those who manufacture No-Clean Paste, Flux, and Cored Wire.
Once a circuit card assembly has been assembled and soldered with No-Clean
products .... Assuming (I know I know...) that the fluxes have been fully
activated,
what type of results should I expect to see....Assuming....that the boards
and components were
"clean" prior to assembly.
More specifically, will Alcohol "reactivate" the no-clean flux or "free"
contaminants that will
register on the Omega Tester?
-Carrie
P.S. And No smart remarks like "How clean is clean" and "You know what
happens when you assume".
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